In recent years, in the development of the design of a product, such as an automobile body, a technique that displays an appearance of a virtual product on a display by using computer graphics (CG) has been used. In order to make the appearance of a virtual product close to the appearance of an actual product, the accurate definitions of reflection characteristics (bidirectional reflectance distribution function (BRDF)) of real paint are important as data for reproducing the appearance of the virtual product.
In order to accurately define a BRDF of a real paint, as hardware and algorithm for quantitatively evaluating the graininess of a metallic color used in a paint of a product, there is proposed a technique in which graininess is represented by three physical quantities of the brightness of high brightness portion, the area of light brightness portion, and the number of high brightness portions, and in which the graininess having a visual correlation is quantified by a multiple linear regression formula using these parameters as explanatory variables (Non-Patent Literature 1).